Intrinsically conducting polymers are of wide utility in applications such as electronic packaging, organic light-emitting diodes (LEDs), electrochromic windows, volatile organic gas sensors, and the like. Intrinsically conducting polymers of particular interest possess a relatively low band gap (Eg), which refers to the energy difference between two electronic energy levels (the conduction band and the valence band). The band gap exhibited by a given polymer depends upon a variety of factors, including the structure of the monomer(s) used to form the polymer. For example, intrinsically conductive polymers formed from thiophene and substituted thiophene monomers are known. Poly(thiophene) has a band gap of 2.1 electron volts (eV), poly(2-decylthieno[3,4-b]thiophene) has a band gap of 0.92 eV, and poly(2-phenylthieno[3,4-b]thiophene) has a band gap of 0.85 eV. Intrinsically conductive polymers comprising polymerized units of thieno[2,3-b]thiophene and thieno[3,2-b]thiophene are also known.
Unfortunately, there are a number of drawbacks associated with many of the intrinsically conducting polymers currently available. The Eg of many polymers is undesirably high, and/or the polymers are not stable. Transparency is difficult to achieve, limiting their use in optical devices. Also of concern is the search for an efficient and inexpensive synthetic route to prepare intrinsically conducting polymers.
There remains a continuing need in the art, however, for intrinsically conducting polymers that exhibit useful band gaps for industrial applications and for the convenient synthesis of such polymers. Furthermore, there is a need for the adjustment of the conductivity and/or optoelectronic properties, such as the band gap and energy levels of the valence band and the conduction band, of such polymers to meet the needs of a particular application.